A wide variety of electrical connectors are available for providing conducting paths between terminal areas or terminal pads on a substrate or a printed circuit daughter board and conductors on a printed circuit mother board or the like. An equally wide variety of terminals are used in these connectors for the many specialized circumstances which are encountered in the electrical and electronics industry. The most common type of terminal used in electrical connectors is the stamped and formed sheet metal type which is manufactured by first stamping a flat blank for the terminal and then bending or forming the blank normally of its own plane to produce the desired configuration in the finished terminal. The terminal will always have a contact portion which engages a terminal pad on the circuit board or substrate and an integral spring means, usually in the form of a spring arm on the end of which the contact portion is located. Since the spring arm is flexed normally of the plane of the metal from which the terminal was formed, a specific terminal can be designed which will satisfy any set of performance characteristics, particularly deflection and contact force, within wide ranges. Because of the fact that the terminal is produced by forming or bending the flat blank after it is stamped, terminals of this type must, as a practical matter, be of some minimum thickness as measured between their oppositely facing sides. The sides of a terminal of this type are usually the edges of the blank and the surfaces extending between the sides were originally surfaces of the stock metal. This restriction that the terminal must have some minimum width for practical manufacturing reasons has not, however, been troublesome in the past under most circumstances.
An alternative type of sheet metal terminal is produced by simply stamping the blank to the form of the finished terminal so that the surfaces of the sheet metal from which the terminal is stamped become the side surfaces of the finished terminal. The thickness of a terminal of this type, which can be described as being coplanar, is then equal to the thickness of the metal stock from which the terminal was produced. In general, complanate terminals can thus be produced in forms which are much thinner than conventional stamped and formed terminals. A shortcoming of previously known coplanar type terminals is that the elements of the terminal, such as the spring means, are relatively stiff and resistant to flexure and to obtain even a small amount of flexure in the terminal, it has been necessary in the past to make the terminals with long, sometimes serpentine spring arms so that the terminal will deflect as desired when it is put to use. Furthermore, the terminal in producing a coplanar type terminal, has been limited with respect to his control over the contact force which will be developed by the terminal in use. Probably because of these shortcomings of flat terminals, their use has been somewhat restricted in the past.
Electrical and electronic equipment of types in limited use at this time and being designed for future use require extremely close spacing of the terminals in the connectors for the equipment, and it is becoming increasingly difficult to design connectors with conventional stamped and formed contact terminals therein, for such equipment. Accordingly, the complanate type terminal is becoming increasingly attractive for these new generations of connectors.
The present invention in accordance with one aspect thereof is directed to the achievement of an improved flat coplanar terminal which overcomes the shortcomings of previous terminals of this type; specifically, the invention is directed to the achievement of a terminal which is capable of a substantial amount of deflection when it is put to use and which will produce a high and precisely predetermined contact force.
In accordance with a further aspect thereof, the invention is directed to the achievement of a terminal which exhibits relatively low self-inductance effects when placed in service. Self-inductance in electrical contact terminals has not been considered a significant problem in the past, for the reason that the switching time for most equipment was relatively long and inductance could therefore be ignored. Electrical equipment now being designed, however, may have switching times of 10.sup.-9 seconds and while the current flowing through an electrical contact may be relatively low, this extremely short switching time can give rise to significant self-inductance effects which may interfere with the proper operation of the equipment. It might be added that self-inductance effects become pronounced if the terminal is designed such that the circuit path through the terminal is relatively long and is other than a straight line. In general, the shorter the circuit path through the terminal, the lower the inductance produced during a switching operation.
One form of electrical contact terminal in accordance with the invention comprises a flat stamped terminal device having a yoke portion from which a latch arm and a spring arm extend. The latch arm is relatively short and has a free end which is adjacent to the yoke portion. The spring arm is relatively long and is provided with a reverse curve intermediate its ends so that it is capable of undergoing substantial deflection, notwithstanding the fact that the terminal is of the flat coplanar type. An edge portion of the spring arm which is adjacent to the free end of the spring arm serves as a contact portion which engages the terminal pad on a substrate or the like, when the terminal is put to use. The free end of the spring arm is against and latched to the free end of the latch arm by means of a latching device which permits the spring arm to flex. The spring arm is furthermore in a stressed and flexed condition, by virtue of the fact that its free end is displaced from the normal position thereof to its latched position against the latch arm. The prestressed condition of the spring arm provides an elevated contact force for the electrical contact with the substrate when the terminal is put to use.